This invention relates to self-inverting water-in-oil emulsions of water-soluble polymers wherein emulsions invert immediately upon the addition of sufficient water. This invention also relates to processes for preparing such emulsions.
Various water-soluble polymers such as polyacrylamide and copolymers of acrylamide with other monomers are well-known to be effective flocculants for many substrates including sewage, cellulosic fibers and fines for retention and freeness, metal or treatment, plating waste, coal tailings, and the like. Such polymers are also known to exhibit superior thickening properties when said polymers are dissolved in aqueous media. Particularly well-known for this purpose are the anionic carboxamide polymers such as acrylamide/acrylic acid copolymers, including those prepared by hydrolysis of polyacrylamide. Such polymers are very useful as fluid mobility control agents in enhanced oil recovery processes.
In the past, such polymers have been made available commercially as powders or finely divided solids which must be subsequently dissolved in an aqueous medium in order to be used. Because such dissolution steps are sometimes time consuming and often require rather expensive mixing equipment, it has become a common practice to formulate the water-soluble polymer in a water-in-oil emulsion wherein the polymer is dissolved in the dispersed aqueous phase. Such emulsions, a well as a method for preparing them, are described in U.S. Pat. No. 3,284,393 to Vanderhoff et al. Unfortunately for many applications, these emulsions do not invert as readily as desired. In order to accelerate the inversion rate of such emulsions, it has been a common practice, e.g., as shown in U.S. Pat. No. Re. 28,474, to add a water-soluble surfactant just prior to inversion. While the addition of an inverting surfactant in this manner does increase the rate of inversion, the resulting emulsions often do not exhibit the activity or ability to pass through porous structures (so-called screen factor or filterability) that is desired for fluid mobility control agents. More importantly, it is found that such practices are generally not satisfactory when it is necessary to invert the emulsion in aqueous medium containing dissolved salts as is often the case for enhanced oil recovery practices.
In view of the foregoing deficiencies of conventional emulsions and methods for inverting them, it is highly desirable to provide a self-inverting water-in-oil emulsion that will invert quickly into an aqueous medium that may contain significant quantities of dissolved salts. It is also desirable to provide an emulsion that has a reduced oil content and increased polymer solids.